CONTEXT: Although calorie loss from increased urinary glucose excretion continues after long-term treatment with sodium-glucose cotransporter 2 inhibitors (SGLT2is), the mechanisms of the attenuated weight loss due to SGLT2is are not well known. OBJECTIVE: To examine the mechanism of the attenuated weight loss during long-term treatment with an SGLT2i, tofogliflozin, focusing on the antilipolytic effect of insulin on adipose tissue. DESIGN AND PARTICIPANTS: An integrated analysis was performed using data from two phase 3 studies of 52 weeks of tofogliflozin administration. The antilipolytic effect was evaluated using adipose tissue insulin resistance (Adipo-IR) calculated from the product of the levels of fasting insulin (f-IRI) and fasting free fatty acids (f-FFAs). RESULTS: Data from 774 patients with type 2 diabetes (mean age, 58.5 years; glycosylated hemoglobin, 8.1%; body mass index, 25.6 kg/m2; estimated glomerular filtration rate, 83.9 mL/min/1.73m2; 66% men) were analyzed. Weight loss plateaued between weeks 24 and 52 after decreasing significantly. f-IRI levels decreased significantly from baseline to week 24, and the decrease was maintained until Week 52. f-FFA levels significantly increased, peaked at week 24, then declined from weeks 24 to 52. Adipo-IR levels declined progressively throughout the 52 weeks (-3.6 mmol/L·pmol/L and -6.2 mmol/L·pmol/L at weeks 24 and 52, respectively; P < 0.001 baseline vs weeks 24 and 52 and week 24 vs week 52). Higher baseline Adipo-IR levels were independently associated with greater weight loss at week 52. CONCLUSION: The improved antilipolytic effect in adipose tissue may attenuate progressive lipolysis, leading to attenuating future weight loss induced by an SGLT2i in patients with type 2 diabetes.